1. Field of the Invention
The present invention relates to molding a disk for optical recording medium such as a compact disk (CD) and a digital video disk (DVD), in particular an air blowing method at the time of being released from a mold and a mold therefor.
2. Background of Related Art
A mold for producing an optical disk such as CD or DVD forms a cavity between a fixed mold and a movable mold, and in order to fix a stamper to at least one of mirror surfaces facing to the cavity, comprises a structure where a stamper holder for holding the inner and outer edges of the stamper to the mirror surface. And, when a molten resin is filled in the cavity, a bit which is formed concentrically and in concavo-convex manner in section formed on the surface of the stamper is transferred to a molded product to make a disk having an information data.
This molding method comprises a process as well as a general injection molding and is carried out by following processes. That is, a mold is fixed to a molding-machine, and after carrying out a mounting arrangement of the mold, a mold closing process for putting a fixed mold and a movable mold together, a mold clamping process for maintaining a clamping-keeping pressure due to increasing a pressure to the molds put together, an injection and filling process for filling the molten resin in the mold, a pressure keeping and cooling process for controlling an injection keeping pressure and cooling the mold, a mold opening process for retreating the movable mold and a molded product taking out process are carried out to finish a series of molding process. As a mold to be used for molding a disk, there is such a mold structure as disclosed in, for example, Japanese patent laid-open No. Hei 5-177672 and Japanese utility model publication No. Hei 7-42682, and in FIGS. 3-5, a sectional view of a partial portion of these molds and a main portion are disclosed.
In the two molds mentioned above, a difference with each other resides in the structure for holding the circumference of the stamper. A holding means shown in FIGS. 3 and 4 is a flat type and the one shown in FIG. 5 is a push-in type. The flat type shown in FIG. 3 is structured from an outer ring comprising an inner ring portion, an outer ring portion and a gas exhausting opening, which is mounted through a resilient member on the side of the mirror plate of a mold opposite to the mold on which a stamper is held and disposed in such a manner as it surrounds the cavity while making its outer ring portion get in touch with the stamper surface.
In the explanation referring to reference signs of FIG. 4, it is of a structure in which an outer ring 50 is mounted on the side of a mirror plate 55 of a movable mold through a conical spring 54 by a bolt 53 inserted in a central hole while the outer ring portion 51 abutting a stamper face 16a and forming a gap 30 between the inner ring portion 52 and the stamper 16. Thereby, at the time of closing the mold, the conical spring 54 is compressed on the mirror plate 55 and the outer ring 50 slides on the side surface of the mirror plate 55 along the axial direction of the bolt 53. On the other hand, at the time of opening of the mold, the outer ring 50 moves reversely in the previous direction due to the restreating force of the conical spring 54. This displacing distance is controlled in a given stroke by the length of the bolt and the conical spring 54. Further, the gap 30 between an inner ring portion 52 of the outer ring and a stamper surface 16a is set in its width so as to be passed by a gas but not by a molten resin. Thereby, the gas only in the cavity is adapted to be exhausted through the gap 30, a gas drain groove 56 and a gas drain opening 57.
Further, in a holding means of the push-in type shown in FIG. 5 too is, as well as in the flat type, formed with an outer ring 60 surrounding the stamper. Conventionally, in this type of a disk mold, at the time of releasing the disk from the stamper 16, an air b from an air passage of a movable mold is supplied through the gap between the stamper holder and a sleeve (not shown). However, it is not easy for a disk to be released in one direction from inside to outside due to the resistance of the existence of a concavo-convex configuration of the stamper, and, merely by this air b (air blow) in the inner side, the disk is not released even from a front face of the stamper and, since an air supply to the outer circumference of a disk is delayed and the releasing balance thereof becomes different between the inside and outside of the disk, a boundary pattern like a mist appears on the disk surface to have generated a problem.
However, in the mold shown in FIG. 5, there are an air a blown from an air passage A of a fixed mold toward the bottom side of the cavity and an air b blown from an air passage B of the movable mold toward the stamper side, in addition an air c is adapted to be blown from the outer side of the disk toward inside of the cavity through an air passage C provided so as to blow an air from the outer side of the disk. Whereby, the gap 30 between the outer ring 60 and the stamper surface 16a does not become exclusive for the gas drain like in the flat type and forms one part of the air passage C through which is formed for the air which is supplied from an air passage 65 opened at a concave portion 64 of the outer ring to the inside of the cavity 3. In addition, in the structure of FIG. 5, a vacuum passage D is formed in order to suck an air d for making the outer circumference of the stamper contact tightly to a mirror plate 66.
Accordingly, the airs a and b supplied through the air passages A and B are blown from the inner circumference of the disk outside of the cavity in the radial direction of the cavity and the air c supplied from the air passage C is blown through the outer ring 60 and the gap 30 between a projected portion from the outer ring and the stamper surface 16a toward the inside of the cavity 3 in the radial direction. As a result, a disk is released from the mirror face of the cavity bottom and the stamper face.
Therefore, in the above mentioned mold structure of the push-in type, an air blow is supplied from both sides in the radial direction, and due to this mold structure an even, complete and instant releasing from the stamper and the sticking by sucking the stamper to the mirror face of the movable mold are simultaneously obtained, so that it becomes possible to prevent the stamper from being floated up unevenly from the mirror face and the uneven defect of the stamper surface from being generated to attain an improvement in the air blow method for releasing the disk from the mold.
However, in the flat type of the structure of the mold, the outer ring is not fixed like in the push-in type, the stamper is pushed through a resilient means and the holding means of the outer circumference of the stamper is adapted to be displaced to and fro at every opening and closing of the mold. Further, there is not provided with the vacuum passage for sucking the stamper to the mirror plate. Therefore, in the flat type, it is difficult to join the passages provided in the mold and since the gap between the stamper surface and the inner ring portion is exclusively used for exhausting the gas, an air supply in the reverse direction could not carry out.
In the light of such situation, the purpose of the present invention is to provide an air blow method and a mold thereof in which by making use of the holding means for holding the outer circumference of the stamper in the flat type as a holding means, a good molding of a disk is carried out.